The invention relates generally to integrated circuits having circuits that provide reference voltages, and more particularly to reference voltage circuits and methods for providing reference voltages circuits that may be single gate oxide circuits and may provide relatively strong immunity to noise and draw low amounts of current.
Submicron technologies for very large scale integration (VLSI) circuits use, for example, 0.25 micrometer, 0.18 micrometer or less gate lengths have very low supply voltages, such as 2.5 V, 1.8 V or lower supplies. Such integrated circuits may include, for example, graphics processing chips, microprocessors and any other suitable integrated circuits. Where the integrated circuits employ MOSFETS or other technology, gate to source and gate to drain voltage potentials have to be maintained within a safe operating level to avoid damage to the circuit elements. However, supply voltages and input signal voltages to circuits that make up the integrated circuit can far exceed the gate to source and gate to drain safe operating voltages. Moreover, where single gate oxide circuits are used, such as where all circuit elements are of a single gate oxide thickness, a designer must typically generate internal reference generated voltage levels that are larger than 0 V but less than the voltage supply level to help provide safe gate to source and gate to drain voltages.
One solution to generate reference voltages within an integrated circuit, includes the use of a simple resistor divider. However, such resistor dividers can consume DC current. This can be a severe drawback where low current requirements are necessary.
Another mechanism to generate additional reference voltages includes using a middle floating point of two circuit elements that in the off condition, avoid current draw, such as serially connected reverse biased diodes. These circuits can provide, for example, a potential one-half of the supply voltage to the serially connected diodes. However, such a configuration can allow noise coupling which changes the potential of the reference level.
Consequently, a need exists for an improved reference voltage generating circuit and method, that has improved noise immunity, and that consumes small amounts of current during operation. It will also be advantageous if such a circuit could be fabricated as a single gate oxide circuit to reduce fabrication complexity.